It has been standard practice in the industry to use a machined brass or steel component, known as a shank mount, to mount a gas valve assembly to a water heater tank. FIG. 6 illustrates a prior art gas valve and shank mount assembly 110 having a gas valve assembly 112 configured to regulate the flow of gas to a water heating system (not shown). A brass shank mount 114 having an interior wall 116, an exterior wall 118 and a central opening 120 is assembled to gas valve assembly 112. An elongate temperature probe assembly 122 is configured to sense the temperature of water in a water heater tank (not shown). The temperature probe assembly 122 includes an invar rod 124 disposed within a copper tube 126, and is assembled to gas valve assembly 112 such that the temperature probe assembly 122 protrudes from the gas valve assembly 112 through the central opening 120 in the brass shank mount 114.
One purpose of this brass shank mount 114 is to provide a mounting means for a temperature sensing probe which is assembled to components configured to open or close the flow of gas in a particular channel of the gas valve assembly 112. Generally, the copper tube 126 and invar rod 124 assembly is configured to be positioned inside the water heater tank. The copper tube 126, having a high thermal coefficient of expansion, expands and contracts as the water temperature in the tank increases and decreases, respectively. The expansion and contraction of the copper tube 126 acts to move the invar rod 124. The invar rod 124 may be configured to push against a lever 128, which causes the gas valve assembly 112 to allow the main gas or bleed gas to flow to the outlet of the valve or to an adjacent gas chamber.
Another purpose of the brass shank mount 114 is to provide a rigid means for mounting the gas valve assembly 112 to the water heater tank using, for example, an external threaded feature on the brass shank mount 114. This allows the gas valve and shank mount assembly 110 to be assembled to the water heater tank and aligned vertically by means of a turning torque. Generally, the gas valve and shank mount assembly 110 is aligned vertically to receive the incoming gas supply. In some cases a relatively high amount of torque is applied to the gas valve and shank mount assembly 110 in order to achieve this vertical alignment.
The temperature set point that is indicated on a temperature dial for the water heating system may be controlled by the position of the lever 128 with respect to the invar rod 124 at a specific water temperature sensed by the copper tube 126. The position of the invar rod 124 with respect to the lever 128 is maintained by the brass shank mount 114 and the copper tube 126. If an excessive amount of torque is used to align the gas valve and shank mount assembly 110 in the vertical position, or if excessive bending moments are applied to the gas valve and shank mount assembly 110, the position of the invar rod 124 may be shifted. That change in position may then affect the temperature calibration of the gas valve and shank mount assembly 110 as set at the factory. It is typical in current brass shank mount designs that a considerable amount of torque (i.e., enough to change the position of the invar rod) may be applied to the brass shank mount 114 during vertical alignment of the gas valve and shank mount assembly 110 on the water heater tank.
A third purpose of the brass shank mount 114 is to provide a water-tight seal between the interior and exterior of the water heater tank. The brass alloys typically used to make the brass shank mount 114 have a low corrosion rate when compared to other metal alloys such as aluminum and steel. Brass is a suitable material for use in containing the high temperature, high pressure water inside the water heater tank. Any substitute material for the brass alloys should be able to withstand the high pressures and temperatures experienced in a water heater tank, and should meet or exceed the low corrosion rate of the brass alloys when exposed to water at such pressures and temperatures.
Brass alloys, however, are expensive when compared to alloys of aluminum and steel. Additionally, brass shank mounts 114 must typically be made in a number of differing lengths and diameters to accommodate the variety of water heater tanks on the market. As such, the particular brass shank mount 114 to be used must typically be fitted to the gas valve assembly 112 before calibration of the temperature probe assembly 122 can be completed. As a result, the calibration step is delayed until the type of water heater to which the gas valve assembly 112 is to be attached is determined. Furthermore, as discussed, gas valve and shank mount assemblies 110 with brass shank mounts 114 may be over-torqued during vertical alignment or the valve. Some of the stresses from over-torquing may be transferred from the brass shank mount 114 to the invar rod 124 changing the temperature calibration of the gas valve and shank mount assembly 110.
It would therefore be useful to have a standard size shank mount for gas valve assemblies so that the temperature probes of all assemblies could be calibrated immediately after production. It would also be useful to have a shank mount assembly which uses less expensive materials than the brass alloys commonly used today, and which does not render the temperature sensing probe on the gas valve assembly as susceptible to calibration shift from over-torquing as machined brass shank mounts.
The embodiments of the invention provide such a solution to one or more of the aforementioned problems. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.